Leakage current or resistance measurement method, and monitoring apparatus and monitoring system of the same

ABSTRACT

A method for measuring the resistance component current included in the leakage current is provided. In a monitoring apparatus and system for measurement the signal waveform of at least one AC cycle is sampled. The resistance component leakage current is measured by dividing the average of integrated value of the instantaneous leakage current values and the instantaneous voltage values by the square root of average of squared instantaneous voltage values. In addition, a voltage signal of the target measurement circuit is obtained the waveform of the leakage current signal and the voltage signal for one cycle is sampled and stored; the leakage current signal and the voltage signal are expanded to N-th higher harmonic wave component respectively, and the resistance component that relates to the leakage current is calculated.

BACKGROUND OF THE INVENTION

This invention relates to a method for measuring the resistancecomponent current included in a leakage current and resistance value,namely insulation resistance to monitor the insulation of a distributionsystem, and relates to an instrument, apparatus, or system to which thismeasurement method is applied.

(A) a direct measurement method in which a zero-phase currenttransformer is provided to a distribution circuit or a groundingconductor of a transformer, (B) a measurement method in which a voltageis applied externally on a grounding conductor of a transformer or adistribution circuit, or (C) a method in which a leakage current ismeasured based on the output of a zero-phase current transformer and thevoltage of a distribution circuit have been proposed as the method formeasurement of the leakage current or insulation resistance of aconventional distribution system.

The exemplary disclosure that belongs to (A) includes Japanese PatentLaid-Open No. H2-129556, the exemplary disclosure that belongs to (B)includes Japanese Patent Laid-Open No. S63-238470, Japanese PatentLaid-Open No. H1-143971, Japanese Patent Laid-Open No. H2-83461,Japanese Patent Laid-Open No. H4-52565, Japanese Patent Laid-Open No.H6-258363, Japanese Patent Laid-Open No. H9-318684, and Japanese PatentLaid-Open No. H11-304855, and the exemplary disclosure that belongs to(C) includes Japanese Patent Laid-Open No. H3-179271, Japanese PatentLaid-Open No. H4-220573, Japanese Patent Laid-Open No. H6-339218,Japanese Patent Laid-Open No. H2001-225247, and Japanese PatentLaid-Open No. H2001-21604.

These disclosures are summarized in FIG. 9.

FIG. 9 is a structural diagram showing a leakage current measurementsystem. In FIG. 9, 40 denotes a transformer, 41 denotes a breaker, 42denotes a primary circuit of a distribution system, 43 a, 43 b, and 43 cdenote loads of electric components, 44 denotes a grounding conductor ofthe transformer 40, 45 denotes an apparatus for measurement of theleakage current based on the received output of a current transformer46, 47 a, 47 b, and 47 c denote electrostatic capacities generated onthe distribution path, 48 a, 48 b, and 48 c denote power switches of theloads 43 a to 43 c, and 49 denotes an electrostatic capacity of a noisefilter provided to the load. 50 denotes a voltage application apparatusfor applying a voltage on the ground conductor 44 of the transformer 40,and 51 denotes the insulation resistance of the load 43 a or theinsulation resistance of wiring of the primary circuit 42 for thepurpose of convenience.

Iz denotes a leakage current of the primary circuit, Ic denotes acapacitative current (reactive component current) that flows in theelectrostatic capacity, and Igr denotes a resistance component current(active component current) that flows in the insulation resistancecomponent.

In FIG. 9, in the above-mentioned measurement method (A), the zero-phasecurrent transformer is provided to the grounding conductor 44 of thetransformer 40 to measure the leakage current. In the measurement method(B), a voltage of about 1 Hz/1 V is applied from the voltage applicationapparatus 50 so that a current does not flow to the electrostaticcapacities 47 a to 47 c to eliminate the effect of the electrostaticcapacity, and a signal generated from the zero-phase current transformer46 is measured by use of the instrument 45. In the measurement method(C), the measurement is carried out based on the voltage applied fromthe primary circuit 42 of the distribution system and the output of thezero-phase current transformer 46.

FIG. 10 is a vector diagram showing the leakage current Iz, thecapacitative that flows in the electrostatic capacity, and theresistance component current that flows in the insulation resistancecomponent. In FIG. 10, the phase angle between the phase voltage and theline voltage is 30 degrees in the case of the three-phase alternatingvoltage. The capacitative current Ic is 90 degrees different from theresistance component current Igr, and the leakage current Iz is thecomposite current of the current Ic and the current Igr, namely vectorsum. However, the capacitative current varies depending on the magnitudeof the loading. For example, when all the loads 43 a to 43 c are loaded,the capacitative current increases as shown with Ic′. As the result, theleakage current Iz changes to Iz′. In other words, the currents Iz′ andIc′ change depending on the variation of the load.

The above-mentioned method (A) is involved in a problem of incapablemeasurement of the resistance component current if the electrostaticcapacity is large due to a noise filter because reactive componentcurrent is predominant.

The above-mentioned method (B) is also involved in a problem of complexsystem structure due to the requirement of external application of avoltage and the requirement of no effect on the loading apparatus.

One exemplary method of the above-mentioned method (C) is involved in aproblem of unsuitability for a plurality of distribution circuitsbecause an auxiliary impedance element is provided and the insulationresistance is determined.

Another exemplary method of the above-mentioned method (C), in which thephase angle is determined to calculate the resistance component currentand resistance value and to further detect the insulation deteriorationphase, is involved in the difficulty in determination of the correctphase angle in the small current region because of the characteristic ofthe current transformer.

SUMMARY OF THE INVENTION

It is one object of the present invention to obtain the highly reliableresistance component current value and the resistance value, namely theinsulation resistance, to solve the above-mentioned problem of theconventional methods. It is the other object of the present invention tomonitor the change of insulation deterioration with time for alarming,to enable to check and keep maintenance, and to prevent sudden failure.

To achieve the above-mentioned objects, the present invention providesthe following methods.

(1) A method for measuring the resistance component current of a targetmeasurement circuit from the signal of a current transformer fordetecting the leakage current of the target measurement circuit and thevoltage signal of the target measurement circuit, wherein the waveformsignal of at least one cycle is sampled, and the resistance componentcurrent is obtained from the result of division of the average of theintegrated value of the instantaneous voltage values and theinstantaneous leakage current values by the square root of average ofsquared instantaneous voltage values.

(2) A method for measuring the resistance component current of athree-phase AC target measurement circuit from the signal of a currenttransformer for detecting the leakage current of the target measurementcircuit and the voltage signal of the target measurement circuit,wherein the waveform signal of at least one cycle is sampled and thevoltage signal is stored, and the resistance component current isobtained from the result of division of the average of integrated valueof the instantaneous value of the leakage current and the instantaneousvalue of the stored voltage signal at the phase angle of 30 degreesadvance by the square root of average of squared instantaneous values ofthe voltage signal.

(3) A method for measuring the resistance component current of athree-phase AC target measurement circuit from the signal of a currenttransformer for detecting the leakage current of the target measurementcircuit and the voltage signal of the target measurement circuit,wherein the waveform signal of at least one cycle is sampled and thevoltage signal is stored, and the resistance component current isobtained from the result of division of the average of integrated valueof the instantaneous value of the leakage current and the instantaneousvalue of the stored voltage signal at the phase angle 30 degrees advanceby the square root of average of squared instantaneous values of thevoltage signal for the three-phases. Each phase voltage of thethree-phases used for calculation of the leakage component current maybe obtained by means of a method in which the line voltage signal of twophases is obtained and the residual one phase voltage is obtained bymeans of the vector arithmetic, or may be obtained by means of a methodin which one line voltage signal is obtained, and the residual two phasevoltage signals are obtained by retarding phase angle of theabove-mentioned voltage signal by 120 degrees and 240 degreesrespectively. Otherwise in the case that the voltage-to-ground is used,the residual one phase voltage may be obtained from thevoltage-to-ground of two lines and the residual one phase voltage isobtained by means of the vector arithmetic, or may be obtained by meansof a method in which the voltage-to-ground of one line is obtained, andthe phase voltage of the residual two phases is obtained by retardingphase angle of the above-mentioned voltage signal by 120 degrees and 240degrees respectively.

(4) The resistance component that relates to the leakage current isobtained by means of a method in which a leakage current signal of an ACcurrent target measurement circuit, a voltage signal of the targetmeasurement circuit, and the waveform of the leakage current signal andthe voltage signal for one cycle are sampled and stored, the leakagecurrent signal and the voltage signal are expanded to N-th higherharmonic wave component respectively, and the resistance component thatrelates to the leakage current is calculated according to thesimultaneous equations based on the assumption that the value obtainedby dividing the leakage current component of the second or higher orderby the voltage component of the same order is regarded to be equal tothe admittance composed of the resistance component of the same orderand the electrostatic capacity component.

(5) The resistance component that relates to the leakage current isobtained by means of a method in which a leakage current signal of an ACcurrent target measurement circuit, a voltage signal of the targetmeasurement circuit, and the waveform of the leakage current signal andthe voltage signal for one cycle are sampled and stored, the leakagecurrent signal and the voltage signal are expanded to N-th higherharmonic wave component respectively, and the resistance component thatrelates to the leakage current is calculated as the result of the phaseangle difference between the leakage current component of at least oneorder obtained from the expansion arithmetic and the voltage componentof the same order.

(6) The resistance component that relates to the leakage current isobtained by means of a method in which a leakage current signal of an ACcurrent target measurement circuit, a voltage signal of the targetmeasurement circuit, and the waveform of the leakage current signal andthe voltage signal for one cycle are sampled and stored, the leakagecurrent signal and the voltage signal are expanded to the DC componentand N-th higher harmonic wave component respectively, and the resistancecomponent that relates to the leakage current is calculated by dividingthe voltage signal DC component obtained from the expansion arithmeticby the leakage current signal DC component obtained in the same manner.

(7) The order to be selected in the above-mentioned (5) and (6) is amultiple of 3 that is suitable for the three-phase AC.

(8) The largest ratio to the basic wave component of N-th higherharmonic wave component of the order to be selected to calculate theresistance component that relates to the leakage current is selectedautomatically for measurement of the resistance component in theabove-mentioned (5) and (6).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a waveform diagram for describing the first embodiment of theleakage current measurement method in accordance with the presentinvention;

FIG. 2 is a waveform diagram for describing the second embodiment of theleakage current measurement method in accordance with the presentinvention;

FIG. 3 is a waveform diagram for describing the first embodiment of theleakage current measurement method in accordance with the presentinvention;

FIG. 4 is a structural diagram showing an embodiment of a leakagecurrent measurement system that uses an instrument in accordance withthe present invention;

FIG. 5 is a structural diagram showing an embodiment of a leakagecurrent measurement system that uses a circuit breaker in accordancewith the present invention;

FIG. 6 is a structural diagram showing an embodiment of a leakagecurrent measurement system that uses a monitoring apparatus inaccordance with the present invention;

FIG. 7 is a structural diagram showing an embodiment of a leakagecurrent measurement system that uses a breaker in accordance with thepresent invention;

FIG. 8 is a characteristic diagram showing the resistance componentcurrent value change with time;

FIG. 9 is a structural diagram showing a leakage current measurementsystem;

FIG. 10 is a vector diagram showing the vector of the leakage current Izof the primary circuit, the capacitative current that flows in theelectrostatic capacity, and the resistance component current that flowsin the insulation resistance component;

FIG. 11 is an apparent view of an insulation monitoring apparatus;

FIG. 12 is an apparent view of another exemplary insulation monitoringapparatus; and

FIG. 13 is a diagram showing an insulation monitoring apparatuscontained in a distribution panel. FIG. 13A is a front view of theinsulation monitoring apparatus and FIG. 13B is a A—A cross sectionalview of FIG. 13A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described in detailhereinafter with reference to the drawings.

FIG. 1 is a waveform diagram for describing the first embodiment of theleakage current measurement method in accordance with the presentinvention, and the principle of calculation of the resistance componentcurrent from the leakage current by use of this waveform diagram. Thewaveform shows a waveform for the case that the primary circuit 42 ofthe distribution system shown in FIG. 9 is a single-phase circuit, inwhich the output of the current transformer 46 and the voltage waveformgenerated from the primary circuit 42 are represented by the time axis.

In FIG. 1, Iz denotes the leakage current, V denotes the voltage, Wdenotes the leakage current power, and dots of each waveform show thesampling value. The phase of the leakage current Iz proceeds 90 degreesahead of the voltage if no active component current Igr is involved.

The power W of the AC circuit is calculated by use of the equation W=VIcos Φ according to the AC theory, wherein V denotes the circuit voltage,I denotes the load current, and cos Φ denotes the phase angle (powerfactor angle) of the voltage and the load current. The instantaneousvalue of the voltage and current waveform for one AC cycle is sampledand the average integrated value of instantaneous voltage values, andinstantaneous load current values is calculated.

As shown in FIG. 10, the active component current Igr is given by theequation Iz cos Φ, wherein the Iz denotes the leakage current. Thisembodiment is characterized in that the power which is replaced with theleakage current Iz instead of the load current I of the equation W=VIcos Φ (leakage current power) is calculated and the power is furtherdivided by the voltage to obtain the active component current Igr.

In other words, W/V=Iz cos Φ=Igr. As the result, the resistancecomponent current (active component current) Igr is obtained. Herein,the voltage means the voltage for one AC cycle, and the voltage isobtained as the square root of the averaged square of sampledinstantaneous voltage values.

As obvious from the above-mentioned equation, the power W and thevoltage V are used as a means for calculating the resistance componentcurrent Igr, and the taken-in voltage V may be arbitrary. It isunderstandable that if the resistance component current included in theleakage current increases in FIG. 1, it comes near to the voltage phaseand the power comes to the positive side.

Next, the second embodiment of the present invention will be describedwith reference to FIG. 2.

FIG. 2 is a waveform diagram for describing the second embodiment of theleakage current measurement method in accordance with the presentinvention, and shows the voltage waveform, leakage current waveform, andleakage current power waveform for the case in which the power issupplied to the load with two-wire drawing from the first phase (RS) ofthe three-phase AC. In this case, the phase of the leakage current Izproceeds 60 degrees ahead of the voltage (line voltage) if only theelectrostatic capacity is involved. The reason is that the line voltagein the three-phase AC proceeds 30 degrees ahead of the phase voltage.Therefore, the second embodiment is characterized in that theinstantaneous line voltage value is stored when the leakage current andthe line voltage are sampled and the power calculated by use of theinstantaneous leakage current value and the stored instantaneous voltagevalue that proceeds 30 degrees advance is obtained, and the power isdivided by the voltage to calculate the resistance component current.Herein, the voltage is also the square root of average of squaredinstantaneous values of one AC cycle as in the case of the firstembodiment.

Next, the third embodiment of the present invention will be describedwith reference to FIG. 3.

FIG. 3 is a waveform diagram for describing the third embodiment of theleakage current measurement method in accordance with the presentinvention, and shows the voltage waveform of the three-phase AC (voltageRS, voltage ST, and voltage TR) and the leakage current waveform Iz ofthe three-phase AC. The voltage of the respective voltage waveforms ofthe three-phase AC is the line voltage. As it is well known, respectiveline voltages proceed with intervals of 120 degrees phase difference.When the leakage current is sampled correspondingly to each voltagewaveform, the leakage current Iz proceeds 60 degrees ahead of the linevoltage as shown in FIG. 3 in the case that only the electrostaticcapacity is involved similarly to the second embodiment. Therefore, theinstantaneous line voltage values are stored when the leakage currentand instantaneous values of each line voltage waveform are sampled, eachpower is calculated by use of the instantaneous leakage current valueand each stored instantaneous voltage value that proceeds 30 degreesadvance, each power is divided by each voltage, the phase that has thepositive maximum value among the resultant quotients corresponds to theinsulation deterioration phase, and this value is regarded as theresistant component current value. Each phase voltage used when theresistance component current of each phase of the three-phase iscalculated may be obtained by means of a method in which line voltagesignals of two phases are obtained and the residual one phase isobtained by the vector arithmetic, or may be obtained by means of amethod in which one line voltage signal is obtained and residual twophases are obtained from the voltage signal obtained as describedhereinabove by retarding the phase angle by 120 degrees and 240 degrees.In the case that the voltage-to-ground is used, the residual one phasemay be obtained by the vector arithmetic by use of the voltage-to-groundof the two lines, or may be obtained by means of a method in which thevoltage-to-ground of one line is obtained and residual two phases areobtained by retarding the phase angle by 120 degrees and 240 degreesfrom the voltage signal obtained as described hereinabove.

Next, the sampling will be described herein under. The sampling meansmeasurement of the waveform for one AC cycle at a predetermined timeintervals, and the predetermined time interval means, for example,0.5556 ms for 50 Hz that is a value obtained by dividing by 36, or 0.463ms for 60 Hz that is a value obtained by dividing by 36.

Next, the fourth embodiment of the present invention will be describedherein under.

According to the above-mentioned embodiments, the input voltage may bearbitrary. The voltage supplied from a target measurement circuit may beconverted to an input voltage value, and the voltage value is divided bythe resistance component current obtained in the first embodiment to thethird embodiment to thereby calculate the resistance value. In otherwords, the insulation resistance value of the target measurement circuitis obtained.

Next, the fifth embodiment of the present invention will be describedwith reference to the equations 1 to 7.

The above-mentioned third embodiment is not suitable for the case inwhich the electrostatic capacity components of respective phases are notbalanced. However, the fifth embodiment is suitable for propercalculation even though the electrostatic capacity components ofrespective phases are not balanced.y(t)=A ₀ +Σa _(n) sin nωt+Σbn cos nωtory(t)=A ₀ +ΣA _(n) sin (nωt+φn)  (Equation 1)whereAn=√an ² +bn ² , φn=tan⁻¹(bn/an)an=2/T∫y·sin nωtdt bn=2/T∫y·cos nωtdt

The equations 1 to 7 are used for describing the fifth embodiment inaccordance with the measurement method of the present invention formeasurement of the resistance component of the leakage current. Theequation 1 represents AC wave that is not a sine wave, namely expansionof a strained wave, which is well known equation as Fourier expansion.In the equation 1, y(t) represents a strained AC voltage or current, A₀represents a DC component, A_(n) sin(nωt+φn) represents a basiccomponent (n=1) and higher harmonic wave components.V=V ₀ +V ₁ sin(ωt+φ1)+V ₂ sin(2ωt+φ2)+V ₃ sin(3ωt+φ3)+ . . .   (Equation2)Iz=I _(z0) +I _(z1) sin(ωt+φ1)+I _(z2) sin(2ωt+φ2)+I _(z3) sin(3ωt+φ3)+. . .   (Equation 3)

The equations 2 and 3 are expansion of the voltage signal and leakagesignal derived from the above-mentioned equation 1. The magnitude of theleft side member y(t) may be replaced with the effective value obtainedas a square root of squared instantaneous values, wherein theinstantaneous voltage waveform signal or leakage current signal issampled as in the embodiments 1 to 3.Y ₃ =V ₃ /I _(z3)  (Equation 4)Y ₉ =V ₉ /I _(z9)  (Equation 5)Y ₃=√(1/R)²+(3ωC)²  (Equation 6)Y ⁹=√(1/R)²+(9ωC)²  (Equation 7)

The equation 4 and the equation 5 represent the admittance of, forexample, third order higher harmonic wave component and ninth orderhigher harmonic wave component of a parallel circuit of a resistancecomponent and electrostatic capacity component formed in thedistribution circuit. The magnitude of the equation 4 and the equation 5is represented by the equation 6 and the equation 7 respectively,wherein R denotes the resistance component, C denotes the electrostaticcapacity component, and ω denotes the angular velocity 2Πf. Therefore,the voltage and current are expanded into the third order higherharmonic wave component and the ninth order higher harmonic wavecomponent by use of the equation 2 and the equation 3, the admittance ofthe third order higher harmonic wave component and the ninth orderhigher harmonic wave component is calculated by use of the equation 4and the equation 5, and the simultaneous equation of the equation 6 andthe equation 7 is solved to thereby obtain the resistance component R ofthe leakage current. The equation 4 and the equation 5 are representedby the admittance, however as a matter of course the value obtained bydividing the second or higher order voltage higher harmonic wavecomponent by the current component of the same order is equal to theimpedance comprising the resistance component and the electrostaticcapacity component of the same order.

Next, the sixth embodiment of the present invention will be describedwith reference to the equation 1 to the equation 10.φvi=tan⁻¹ Vb ₃ /Va ₃−tan⁻¹ Ib ₃ /Ia ₃  (Equation 8)

-   -   φvi: Phase difference between third order higher harmonic wave        voltage and current        W ₃ =Iz ₃ ·V ₃ cos φvi  (Equation 9)        R=V ₃ ² /W ₃  (Equation 10)

The equations 8 to 10 are used for describing the sixth embodiment inaccordance with the measurement method of the present invention formeasurement of the resistance component due to the leakage current. Theequation 8 is used to calculate the phase angle difference between thevoltage phase and the current phase based on the voltage phase as thereference for φn in the above-mentioned equation 1. For example, theabove-mentioned phase angle difference is the difference between thephase angle of the voltage and the current of the third order higherharmonic wave component calculated based on the equation 2 and theequation 3. The equation 9 is used to calculate the power of the thirdorder higher harmonic wave component from the phase angle differencecalculated by use of the above-mentioned equation 8 and, for example,the voltage and current of the third order higher harmonic wavecomponent calculated by use of the above-mentioned equation 2 and theequation 3. The equation 10 is used to calculate the resistancecomponent due to the leakage current from the above-mentioned equation 9and the equation 2. The resistance component is calculated by use of thethird order higher harmonic wave component in the present embodiment,however as a matter of course the resistance component can be calculatedby use of other higher harmonic wave components.

Next, the seventh embodiment of the present invention will be describedherein under.

The first term of the right side members that is the DC currentcomponent A₀ of the above-mentioned equation 1 is pertinent to a case inwhich the average of both positive and negative waves in one AC cycle isnot equal to 0. The case does not happen in an AC circuit exceptingrushing of load, however, insulation deterioration in a circuit causesthe average value that is not equal to 0 and causes the direct currentcomponent. Therefore, the same method as used in the sixth embodiment inwhich the DC component of the voltage is divided by the DC component ofthe leakage current may be applied to calculate the resistance componentdue to the leakage current by use of the higher harmonic wave component.

Next, the eighth embodiment of the present invention will be described.

The third order higher harmonic wave component and the ninth orderhigher harmonic wave component are used in the fifth embodiment, and thethird order higher harmonic wave component is used in the sixthembodiment exemplarily. However, it is not required to carry out storingand calculation on each phase as done in the third embodiment becausethe phase deviation between respective phases is 120 degrees in the caseof the three-phase AC and the higher harmonic wave components of eachphase of the orders of multiple of 3 appear at the same positionadditionally. Therefore, as a matter of course the calculation iscarried out on one phase and division by the order component is carriedout to calculate the resistance component due to the leakage current.

Next, the ninth embodiment of the present invention will be describedherein under.

The wave is expanded to N-th order higher harmonic wave component, forexample, the third or ninth order higher harmonic wave component in thefifth embodiment, and the wave is expanded to the third order higherharmonic wave component in the sixth embodiment to calculate theresistance component due to the leakage current. However, if the smallvalue is obtained by expansion, the order limitation can result in poorreliability. To avoid such problem, the order having the largerproportion to the basic wave component is automatically selected fromamong the expanded N-th order higher harmonic wave components forcalculation in the ninth embodiment.

Next, the tenth embodiment of the present invention will be describedherein under.

The wave is expanded to, for example, the third or ninth order higherharmonic wave component in the fifth embodiment and the wave is expandedto the third order higher harmonic wave component in the sixthembodiment to calculate the resistance component due to the leakagecurrent. However, the small higher harmonic wave component can result inpoor reliability of the value obtained by expansion. To avoid suchproblem, the resistance component due to the leakage current iscalculated by means of the method of the fifth embodiment or the sixthembodiment if the proportion to the basic wave component of the higherharmonic wave component is equal to or larger than a predeterminedvalue, and on the other hand the resistance component due to the leakagecurrent is calculated by means of any one method of the first embodimentto the fourth embodiment if the proportion to the basic wave componentof the higher harmonic wave component is smaller than the predeterminedvalue. The calculation method is selected automatically. This embodimentis suitable for, for example, the extremely small voltage higherharmonic wave.

Next, the eleventh embodiment of the present invention will be describedherein under.

The DC current component is used to calculate the resistance componentdue to the leakage current in the seventh embodiment in the seventhembodiment. However, the reliability of the value obtained bycalculation can be poor if the DC current component is extremely small.To avoid such problem, the resistance component due to the leakagecurrent is calculated by means of the method of the seventh embodimentif the proportion to the basic wave component of the DC currentcomponent is equal to or larger than a predetermined value, and on theother hand the resistance component due to the leakage current iscalculated by means of the method of the fourth embodiment if theproportion to the basic wave component of the DC current component issmaller than the predetermined value in the eleventh embodiment. Thisembodiment is suitable for, for example, the extremely small voltagehigher harmonic wave.

Next, the twelfth embodiment of the present invention will be describedby use of the equation 11.Igr=V ₃ /R  (Equation 11)

The equation 11 involves a method in which the voltage waveform signalis sampled for one AC cycle and the square root of squared instantaneousvalues, namely the effective value of the voltage signal, is divided bythe resistance component obtained in the fifth embodiment to theeleventh embodiment to thereby calculate the resistance component due tothe leakage current.

Next, the thirteenth embodiment of the present invention will bedescribed herein under.

The above-mentioned leakage current Iz of the primary circuit includesthe capacitative current Ic that flows to the electrostatic capacitycomponent and the resistance component current Igr that flows to theinsulation resistance component, and circulates to the groundingconductor of the transformer 40 through the ground. The current causes avoltage between the primary circuit and the ground. Therefore, theresistance component current or resistance value can be calculated byobtaining the voltage-to-ground between one phase line of the targetmeasurement circuit and the ground based on the voltage signal taken inthe above-mentioned embodiments. If the voltage-to-ground is used, thevoltage-to-ground of the residual one phase may be calculated by meansof the vector arithmetic based on the voltage-to-ground of two lines, ormay be calculated by means of a method in which the voltage-to-ground ofone line is obtained and the voltage-to-ground of the residual twophases is obtained by retarding the phase angle by 120 degrees and 240degrees from the voltage signal obtained as described hereinabove.

Next, the fourteenth embodiment of the present invention will bedescribed herein under.

FIG. 4 is a structural diagram showing an exemplary leakage currentmeasurement system that uses a measurement instrument in accordance withthe present invention. In FIG. 4, 1 denotes a measurement instrument,which is used also as a monitoring apparatus. The measurement instrumentor monitoring apparatus 1 is provided with following components. 2denotes a non-contact type current detector for measurement of theleakage current of a target measurement circuit, 3 denotes a signal lineof the current detector, 4 denotes a voltage supply line, which isserved also as a signal line, for supplying a suitable voltage to apower source unit 5 that supplies a voltage to the inside of themeasurement instrument or monitoring apparatus 1, 6 denotes a input unitfor converting the output received from the signal lines 3 and 4 to thesuitable internal signal, 7 denotes an A/D converter unit for samplingand converting the output of the input unit 6 to the digital value inresponse to the command received from the arithmetic processing unit 8that will be described hereinafter, and 8 denotes the arithmeticprocessing unit that is served for commanding the A/D converter unit 7to sample a signal and convert it to a digital value, for commanding amemory unit 9 to store the obtained digital value therein, and forcalculating the resistance component current and the resistance value bymeans of any one of the methods described in the first embodiment 1 tothe thirteenth embodiment. Furthermore, the arithmetic processing unit 8also supplies the resistance component current value that is obtained asthe result of calculation to an output unit 10. The output unit 10visually displays the calculation result obtained by means of thearithmetic processing unit 8 by use of a display apparatus or transmitsthe calculation result to remote sites.

In this embodiment, the voltage V supplied from the signal line (thecircuit voltage is a single phase or single-phase three-lines, or twoline drawing from three-phase three-lines) or the voltage RS and theleakage current Iz obtained from the leakage current detector 2, namelythe vector sum of the capacitative current Ic and the resistancecomponent current Igr, is supplied, the vector sum is converted to adigital value by means of the A/D converter unit 7, the converted vectorsum is subjected to arithmetic by means of the arithmetic processingunit 8, and the resistance component current (active component current)or the resistance value of the insulation resistance is calculated. Asthe result, the resistance component current and the resistance valueare obtained by means of the method described in the first to thirteenthembodiments.

Next, the fifteenth embodiment of the present invention will bedescribed with reference to FIG. 5.

FIG. 5 is a structural diagram showing an exemplary leakage currentmeasurement system that uses a circuit breaker in accordance with thepresent invention. The circuit breaker 11 comprises an off/on mechanicalunit 14 and a leakage measurement unit. In the on/off mechanical unit14, 12 denotes a cable way that connects the receiving end of thetransformer 40 side to the supply end terminal of the load 43 side, andthe cable way is opened/closed by means of the on/off mechanical unit14. Furthermore, the on/off mechanical unit 14 comprises a breaker unit27, a current transformer 15 for detecting a current, an overcurrentdetection unit 16 for detecting overcurrent in response to a signalsupplied from the current transformer 15 for detecting a current, and aturning out apparatus 17 for shutting down the breaker unit 27.

In the measurement unit, 20 denotes a non-contact type current detectorfor measurement of the leakage current of the cable way, 18 denotes abuilt-in step-down transformer of the breaker 11, 19 denotes a powersource unit for supplying a suitable voltage to the inside, 21 denotesan input unit for receiving the output of the current detector 20 andthe transformer 18 and for converting it to a suitable internal signal,22 denotes an A/D converter unit for sampling the output of the inputunit 21 and for converting the output to a digital value when a commandof the arithmetic processing unit 23 described next is received. 23denotes the arithmetic processing unit that supplies a sampling commandand digital conversion command to the A/D converter unit 22, stores theobtained digital value in the memory unit 24, and calculates theresistance component current and the resistance value by means of anyone of the methods described in the first embodiment to the twelfthembodiment. Furthermore, the arithmetic processing unit 23 supplies theresistance component current value that is the calculation result to anoutput unit 25, which will be described hereinafter. The output unit 25visually displays the calculation result obtained by means of thearithmetic processing unit 23 on a display apparatus, or transmits thecalculation result to remote sites. For example, a display apparatushaving six digit segment display apparatus comprising an aggregate oflight emitting diodes (LED element) or a power-saving liquid crystaltype display apparatus may be used as the visual display apparatus fordisplaying the leakage current value and the resistance value.

Otherwise, as the remote transmission, the transmission method based onRS-232C and RS-485 standard that is American Industrial Association(EIA) Standard or the wireless transmission that uses radio wave orinfrared ray may be used.

In the above-mentioned structure, the voltage V (the circuit voltage isa single phase or single-phase three-lines, or two line drawing fromthree-phase three-lines) or the voltage RS and the leakage current Izare supplied to the input unit 21, and subjected to arithmetic by meansof the arithmetic processing unit 23. As the result, the current valueof the resistance component current and the resistance value areobtained. As described hereinabove, the resistance component current andthe resistance value are obtained by means of the above-mentionedstructure and any one of the methods described in the first embodimentto the twelfth embodiment.

Next, the sixteenth and seventeenth embodiments of the present inventionwill be described herein under with reference to FIG. 6 and FIG. 7.

FIG. 6 is a structural diagram showing another embodiment of a leakagecurrent measurement system that uses a monitoring apparatus inaccordance with the present invention. FIG. 6 shows a system comprisinga measurement instrument or monitoring apparatus and a host apparatus,the structure of the measurement instrument or monitoring apparatus isthe same as that shown in FIG. 4. The same components as shown in FIG. 4are given the same characters, and the description is omitted.

FIG. 7 is a structural diagram showing another embodiment of a leakagecurrent measurement system that uses a breaker in accordance with thepresent invention. The structure of the breaker 11 is the same as thatshown in FIG. 5. The same components as shown in FIG. 5 are given thesame characters, and the description is omitted.

Herein, the host apparatus 31 is, for example, a personal computer, andan output unit 10 and a communication means connect the host apparatus31 to the above-mentioned measurement instrument or monitoring apparatus(terminal apparatus) 1 or the breaker 11. The output unit 10 is the sameas the above-mentioned output unit 25. Furthermore, the host apparatus31 stores or displays the information obtained from the terminalapparatus 1 or the breaker 11. The information means the resistancecomponent current and the resistance value. Therefore, the hostapparatus 31 also displays the change of the resistance componentcurrent value and the resistance value with time graphically.

In the above-mentioned description, the system having a singlemeasurement instrument or monitoring apparatus and breaker 11 isdescribed, however, a plurality of terminal apparatus 1 or breakers maybe used without problem. The above-mentioned system may be a systemhaving terminal apparatus such as measurement instrument, monitoringapparatus, and breakers combinedly.

Next, the eighteenth and nineteenth embodiments are described withreference to FIG. 6 and FIG. 7.

FIG. 6 shows a measurement instrument or monitoring apparatus 1 having asetting unit 30, and FIG. 7 shows a breaker 11 having a setting unit 32.The setting units 30 and 32 are served to set a value such as alarminglevel value. The set value is compared with a measured value, and if themeasured value exceeds the set value, an alarm is generated. Forexample, the measure resistance component current is compared with analarming level in the first to third embodiments or the fifth tothirteenth embodiments. For example, a built-in relay contact of theoutput unit 25 is closed to thereby generate an alarm sound, display analarm image, or transmit an alarm signal to remote sites throughcommunication line.

Next, the twentieth embodiment will be described. The content of theoutput supplied to the relay contact in the eighteenth and nineteenthembodiments remains as it was. For example, in the case that the relayis turned on due to the resistance component current value that exceedsthe set value, the relay is remaining in ON-state until an ascertainmentkey of the setting unit 30 or 32 is operated. This system is useful tofind out the cause of the trouble after an alarm is generated as theresult of comparison with the alarming level, and the trouble isrestored. Therefore, it is easy to find out the cause of the trouble.

Next, twenty-first embodiment will be described.

The setting units 30 and 32 are served to set a set value that is avalue for comparison as described in the eighteenth and nineteenthembodiments, and the setting is operated by means of the host apparatus31 having a communication means. Thereby, such system allows the staffnot to go to the setting site for setting work because the setting unitcan be set by remote communication, and the setting work can be doneefficiently.

Next, the twenty-second embodiment will be described with reference toFIG. 8.

FIG. 8 is a characteristic diagram showing the change of the resistancecurrent value with time. The abscissa represents the time, and theordinate represents the resistance component current value (mA). It isthe object of the present invention to measure the resistance componentcurrent included in the leakage current or the resistance value so as todetermine the insulation deterioration state. Generally, insulationdeterioration proceeds very slowly over a long time not within a shorttime. Therefore, if the time of reaching to the predetermined alarmlevel (alarm value) is predicted, the power supply interruption can beplanned previously for replacing the deteriorated insulation parts, andthe sudden failure can be prevented.

It is possible to predict the deterioration by monitoring a graph thatshows the change of the resistance component current value with timeuntil now and to predict the change of the resistance component currentthat will be after a predetermined time.

In FIG. 8, it is assumed that the resistance component current valuebegins to increase at the time t0 and increases by ΔIgr at the time t1,and the alarm value of the resistance component current value Igr is Iq.it is possible to predict that the resistance component current valuewill reach to Iq around t2 based on the resistance component changeduring the time t0 to t1.

The resistance component current is not necessarily stable and involvedin dispersion problem to cause difficulty in the prediction. However,the resistance component current is preferably predicted by means of themethod of least squares that is the demand monitoring technique of thedistribution system, which is disclosed in Japanese Patent Laid-Open No.2000-014003 applied by the inventors of the present invention. Thismethod is served to predict the power consumption that will be afterresidual time T. On the other hand in this embodiment, a set value(alarm value) Iq of the resistance component current value Igr that isset previously is set instead of the power (Q), and the residual time(T) is determined reversely. In detail, the resistance component currentΔIgr is measured and stored at a plurality of time points between thecurrent time point t1 and the time point before Δt shown in FIG. 8, andthe time period T during which the resistance component current reachesto the set value (alarm value) Q point is predicted.

The leakage current Ix that is in a dangerous region is predicted byemploying this method, and the time period during which the leakagecurrent reaches to Ix is predicted.

The time period during which the resistance component leakage currentreaches to the alarm level (alarm value) is predicted by means of theabove-mentioned method. In the above, the set value is a resistancecomponent current, but it is apparent that the set value may be aresistance value.

Next, the twenty-third embodiment will be described.

In the eighteenth and nineteenth embodiments, the alarm signal isone-way communicated from the measurement instrument, monitoringapparatus 1, or breaker 11 to the host apparatus 31. However, two-waycommunication maybe preferably employed for easy mutual communication.In detail, the host apparatus 31 requests the information to a pluralityof terminal apparatus of the monitoring apparatus successively asrequired, and the terminal apparatus transmit the information to thehost apparatus 31 in response to the request. As the result, collisionof communication signals is prevented.

Next, the twenty-fourth embodiment will be described.

The communication employed in the eighteenth and nineteenth embodimentsis wire communication generally. However, a lot of laying work isrequired for the wire communication. To avoid such laying work, theradio communication, namely wireless communication, is employed in thisembodiment. According to this method, the laying work is reducedsignificantly.

Next, the twenty-fifth embodiment will be described.

The memory units 9 and 24 are used in the fourteenth embodiment to thenineteenth embodiment shown in FIG. 4 to FIG. 7 to store the sampledvoltage value mainly. In this embodiment, the resistance componentcurrent or the resistance value that is the calculation result is storedat a predetermined interval in the memory units 9 and 24, and the storedvalue is read out as required. According to this embodiment, the pastdata can be referred and is used effectively for data analysis.

Next, the twenty-sixth embodiment will be described.

FIG. 11 is an apparent view of a monitoring apparatus, which is providedin a distribution panel as described herein under. In FIG. 11, 60denotes a box for containing components, 61 denotes a terminal table forconnecting a current signal line 3 and a voltage signal line 4 extendingfrom a current transformer 20, 62 denotes a setting unit for setting thealarm level and the ratio of current transformation, for selecting aplurality of inputs, and for switching the display type, and 63 denotesa display unit for displaying the value at the setting, and fordisplaying the leakage current value and the resistance value that areobtained as the result of operation of an arithmetic processing unit.

FIG. 12 is an apparent view of a monitoring apparatus, which is mountedon the panel surface of a distribution panel. In FIG. 12, 64 denotes abox for containing components, 65 denotes a terminal table forconnecting a current signal line 3 and a voltage signal line 4 extendingfrom a current transformer 20, 66 denotes a setting unit for setting thealarm level and the ratio of current transformation, for selecting aplurality of inputs, and for switching the display type, 67 denotes adisplay unit for displaying the value at the time of setting, and fordisplaying the leakage current value and the resistance value that areobtained as the result of operation of an arithmetic processing unit,and 68 denotes a bolt for fixing on the panel surface 69 of thedistribution panel.

FIG. 13 is a view showing the monitoring apparatus contained in thedistribution panel.

In FIG. 13, 70 denotes a distribution panel body, 60 a denotes a case,60 b denotes a door, and 60 c denotes aback plate. 71 denotes a maincircuit breaker of the distribution circuit, 72 denotes a branchingbreaker of the distribution circuit, 73 denotes a duct for containingarranged wirings, 74 denotes a duct for containing arranged main circuitwirings of the distribution circuit, and 75 denotes a monitoringapparatus of the type contained in the distribution panel.

Herein the monitoring apparatus shown in FIG. 11 is an apparatus of thetype that is contained in a distribution panel. The size of the box 60is 206 mm×142 mm.

The monitoring apparatus shown in FIG. 12 is an apparatus of the typethat is mounted on the panel face of a distribution panel. The size ofthe box is 206 mm×142 mm. Such monitoring apparatus as describedhereinabove having one side of about 200 mm and the other side in arange from 100 mm to 200 is smaller than the conventional monitoringapparatus and the space for installing a monitoring apparatus is saved,and the monitoring apparatus can be contained in a distribution panelthat is used generally.

The depth size of an monitoring apparatus, particularly the height of aterminal table, corresponds to the height of the above-mentioned duct73. A duct having height of 60 mm popularly used as shown in the A—Across sectional view of the distribution panel. Therefore, a terminaltable having a height of about 60 mm to 80 mm brings about easy wiring,namely improved workability, and the appearance after wiring isimproved.

Furthermore, the width and height of a monitoring apparatus relates tothe outside dimension of a distribution panel, a monitoring apparatushaving the outside dimension as shown in FIG. 11 can be contained in afree space of a distribution panel, and a distribution panel having aconventional dimension can be used.

As described hereinabove, according to the present invention, theresistance component current can be measured even if the electrostaticcapacity of the load of a wiring circuit is large.

Furthermore, because it is not necessary to apply an external voltage,the load component is not affected adversely.

Furthermore, a monitoring apparatus has the simple structure, does notrequire an auxiliary impedance element, and can be applied to aplurality of distribution circuits.

Because it is possible to measure the reliable high resistance componentcurrent value and the resistance value and to specify the insulationdeterioration phase, the monitoring apparatus is useful for check andmaintenance and brings about prevention of failure by monitoring thechange of insulation deterioration with time and by generating alarmwhen required.

1. A leakage current measurement method comprising the steps of:obtaining a leakage current signal of a target measurement circuit;obtaining a voltage signal of said target measurement circuit; andconducting the processing in which the waveform of said leakage currentsignal and said voltage signal for one AC cycle is sampled, and theresistance component current is calculated from the result obtained bydividing the average of integrated value of instantaneous values of saidvoltage signal and instantaneous values of said leakage current signalby the square root of average of instantaneous values of said voltagesignal.
 2. A leakage current measurement method comprising the steps of:obtaining a leakage current signal of a three-phase AC targetmeasurement circuit; obtaining a voltage signal of said targetmeasurement circuit; sampling the waveform of said leakage currentsignal and said voltage signal for one cycle and for storing saidvoltage signal; and calculating the resistance component current bydividing the average of integrated value of instantaneous values of theleakage current and instantaneous values of said stored voltage signalat the phase angle of 30 degrees advance by the square root of averageof squared instantaneous values of said voltage signal.
 3. A leakagecurrent measurement method comprising the steps of: obtaining a leakagecurrent signal of a three-phase AC target measurement circuit; obtaininga voltage signal of said target measurement circuit; sampling thewaveform of said leakage current signal and said voltage signal for onecycle and for storing said voltage signal; and calculating theresistance component current by dividing the average of integrated valueof instantaneous values of the leakage current and instantaneous valuesof said stored voltage signal at the phase angle of 30 degrees advanceby the square root of average of squared instantaneous values of saidvoltage signal for the respective phases.
 4. A monitoring apparatuscomprising: an input unit for receiving the output of a currenttransformer for detecting the leakage current of a target measurementcircuit; an A/D converter unit for converting the output of said inputunit to a digital value; a memory unit for storing the value that hasbeen converted by said A/D converter unit; an arithmetic processing unitfor calculating said leakage current and for conducting the arithmeticprocessing; and an output unit for supplying the arithmetic result ofsaid arithmetic processing unit, wherein said arithmetic processing unitincludes: a means for obtaining a leakage current signal of a targetmeasurement circuit; a means for obtaining a voltage signal of saidtarget measurement circuit; and a means for conducting the processing inwhich the waveform of said leakage current signal and said voltagesignal for one AC cycle is sampled, and the resistance component currentis calculated from the result obtained by dividing the average ofintegrated value of instantaneous values of said voltage signal andinstantaneous values of said leakage current signal by the square rootof average of instantaneous values of said voltage signal.
 5. Amonitoring apparatus comprising: an input unit for receiving the outputof a current transformer for detecting said leakage current of a targetmeasurement circuit; an A/D converter unit for converting the output ofsaid input unit to a digital value; a memory unit for storing the valuethat has been converted by said A/D converter unit; an arithmeticprocessing unit for calculating said leakage current and for conductingthe arithmetic processing; and an output unit for supplying thearithmetic result of said arithmetic processing unit, wherein saidarithmetic processing unit includes: a means for obtaining a leakagecurrent signal of a three-phase AC target measurement circuit; a meansfor obtaining a voltage signal of said target measurement circuit; ameans for sampling the waveform of said leakage current signal and saidvoltage signal for one cycle and for storing said voltage signal; and ameans for calculating the resistance component current by dividing theaverage of integrated value of instantaneous values of said leakagecurrent and instantaneous values of said stored voltage signal at thephase angle of 30 degrees advance by the square root of average ofsquared instantaneous values of said voltage signal.
 6. A monitoringapparatus comprising: an input unit for receiving the output of acurrent transformer for detecting said leakage current of a targetmeasurement circuit; an A/D converter unit for converting the output ofsaid input unit to a digital value; a memory unit for storing the valuethat has been converted by said A/D converter unit; an arithmeticprocessing unit for calculating said leakage current and for conductingthe arithmetic processing; and an output unit for supplying thearithmetic result of said arithmetic processing unit, wherein saidarithmetic processing unit includes: a means for obtaining a leakagecurrent signal of a three-phase AC target measurement circuit; a meansfor obtaining a voltage signal of said target measurement circuit; ameans for sampling the waveform of said leakage current signal and saidvoltage signal for one cycle and for storing said voltage signal; and ameans for calculating the resistance component current by dividing theaverage of integrated value of instantaneous values of said leakagecurrent and instantaneous values of said stored voltage signal at thephase angle of 30 degrees advance by the square root of average ofsquared instantaneous values of said voltage signal for the respectivephases.
 7. A monitoring system for monitoring said leakage currentcomprising: a monitoring apparatus including: an input unit forreceiving the output of a current transformer for detecting said leakagecurrent of a target measurement circuit; an A/D converter unit forconverting the output of said input unit to a digital value; a memoryunit for storing the value that has been converted by said A/D converterunit; an arithmetic processing unit for calculating and operating saidleakage current having a means for obtaining a leakage current signal ofa target measurement circuit, a means for obtaining a voltage signal ofsaid target measurement circuit, and a means for conducting theprocessing in which the waveform of said leakage current signal and saidvoltage signal for one AC cycle is sampled, and the resistance componentcurrent is calculated from the result obtained by dividing the averageof integrated value of instantaneous values of said voltage signal andinstantaneous values of said leakage current signal by the square rootof average of instantaneous values of said voltage signal; and an outputunit for supplying the arithmetic result of said arithmetic processingunit, and a host apparatus for storing and displaying the informationobtained from said monitoring apparatus.
 8. A monitoring system formonitoring said leakage current comprising: a monitoring apparatusincluding: an input unit for receiving the output of a currenttransformer for detecting said leakage current of a target measurementcircuit; an A/D converter unit for converting the output of said inputunit to a digital value; a memory unit for storing the value that hasbeen converted by said A/D converter unit; an arithmetic processing unitfor calculating and operating said leakage current having a means forobtaining a leakage current signal of a three-phase AC targetmeasurement circuit, a means for obtaining a voltage signal of saidtarget measurement circuit, a means for sampling the waveform of saidleakage current signal and said voltage signal for one cycle and forstoring said voltage signal, and a means for calculating the resistancecomponent current by dividing the average of integrated value ofinstantaneous values of said leakage current and instantaneous values ofsaid stored voltage signal at the phase angle of 30 degrees advance bythe square root of average of squared instantaneous values of saidvoltage signal; and an output unit for supplying the arithmetic resultof said arithmetic processing unit, and a host apparatus for storing anddisplaying the information obtained from said monitoring apparatus.
 9. Amonitoring system for monitoring said leakage current comprising: amonitoring apparatus including: an input unit for receiving the outputof a current transformer for detecting said leakage current of a targetmeasurement circuit; an A/D converter unit for converting the output ofsaid input unit to a digital value; a memory unit for storing the valuethat has been converted by said A/D converter unit; an arithmeticprocessing unit for calculating and operating said leakage currenthaving a means for obtaining a leakage current signal of a three-phaseAC target measurement circuit, a means for obtaining a voltage signal ofsaid target measurement circuit, a means for sampling the waveform ofsaid leakage current signal and said voltage signal for one cycle andfor storing said voltage signal, and a means for calculating theresistance component current by dividing the average of integrated valueof instantaneous values of said leakage current and instantaneous valuesof said stored voltage signal at the phase angle of 30 degrees advanceby the square root of average of squared instantaneous values of saidvoltage signal for the respective phases; and an output unit forsupplying the arithmetic result of said arithmetic processing unit, anda host apparatus for storing and displaying the information obtainedfrom said monitoring apparatus.